Former president Bill Clinton is scheduled this week to undergo the heart surgery that about 300,000 Americans confront each year when their coronary arteries become dangerously clogged.

Clinton was hospitalized in New York on Friday after he reported chest pain Thursday night and was tested near his suburban home in Chappaqua. After more tests, he was admitted to New York-Presbyterian Hospital, and doctors announced they would need to perform the bypass surgery.

Although the former president had no history of heart disease, he has long dealt with fast-food cravings and had an elevated cholesterol level when he left office in early 2001. During his last presidential physical, Clinton's "bad" cholesterol measured 177 -- doctors now recommend a target score of under 70, by means of diet, exercise or, if necessary, medication.

Cardiologists say chest pains can arrive abruptly. Age, cholesterol and being overweight are the prime culprits in developing heart disease.

"This is a disease that is unfortunately very silent, and most events -- 50 percent of coronary events -- come out of the blue, without any kind of warning," said Valentin Fuster, director of the cardiovascular institute at Mount Sinai School of Medicine in New York. "In his case, I don't think it is an unusual case."

If his procedure follows the usual pattern, Clinton, 58, will be sedated early in the morning and brought into an operating room. According to surgeons who perform heart bypass surgeries, anesthesiologists will hook him up to several intravenous lines and monitoring catheters and then put him under.

The 42nd president will then be painted from his neck to his ankles with an anesthetic solution that contains an iodine-based compound to reduce the risk of infection.

With the former president fully anesthetized, a surgeon will cut open his chest from the neck down to the breastbone, parting the rib cage, said Paul J. Corso, chief of cardiac surgery at Washington Hospital Center.

In the most common type of operation, Corso said, surgeons administer heparin to reduce the risk of blood clots. The heart is then surgically disconnected from the blood circulation system -- oxygen-poor blood is shunted out of the body before it reaches the heart, purified and cooled by a heart-lung machine and then pumped into the arteries that supply the rest of the body and the brain.

Surgeons then inject a solution of cooled blood and potassium that stops the heart -- although the organ is no longer beating, it is still alive, but at a low energy level.

Typically, tests performed earlier will have told surgeons which arteries are blocked. In some cases, Corso said, several may be impaired, leaving the organ starved of oxygen. Chest pain, or angina, is usually the result of such blockages. Left untreated, they can eventually damage the heart muscle -- in other words, cause a heart attack.

Bypass surgery essentially restores the muscle's blood supply, replacing the clogged arteries with new ones.

"It's like creating a bypass around a blocked pipe," said Jeremy Ruskin, director of the cardiac arrhythmia service at Massachusetts General Hospital. "If you choose not to fix the pipe, you can run a conduit from a point prior to the blockage and reintroduce it to the point after the blockage."

Surgeons typically peel off one end of the left internal mammary artery, which normally supplies blood to the tissues of the chest wall, and connect it to the coronary artery beyond the point of blockage, Ruskin said. Alternatively, a vein from the leg can be used as the shunt -- but grafts using arteries are better able to withstand pressure, can last longer and are believed to have a lower risk of developing constrictions themselves.

Most patients get three to four bypasses during a single operation, and one mammary artery can be used to create two to three bypasses, depending on where the constrictions are, Corso said.

Once the bypasses are completed, warm blood is allowed to flow again into the heart, which usually starts beating on its own. After giving the organ some time to relax, the heart-lung machine is removed, the heart starts pumping blood through the body, and the chest is closed.

There is a second type of bypass surgery -- beating-heart surgery -- in which the heart is not disconnected from the blood circulation during the operation. Instead, surgeons pinch off sections of the organ, stabilizing them long enough to create the shunts and attachments. The procedure is typically more complicated, but it may have a lower risk of stroke among older patients, Corso said.

"The risk of major complications -- stroke, death, paralysis -- is about 3 to 4 percent" in bypass surgery that uses the heart-lung machine, said Ramin Oskoui, a cardiologist at Washington Hospital Center. That is in someone who is in good health, is not diabetic and has good heart muscle function.

"With beating-heart [surgery], the risk of stroke is substantially reduced by a factor of 10. . . . You've cut the risk of major complications by about half and also enhance recovery substantially."

Oskoui said the risk of death as a result of bypass surgery is about 1 to 2 percent.

Convalescence takes a few weeks, but patients are usually out of pain in about 10 days, Corso said.

Sen. Hillary Rodham Clinton (D-N.Y.) discusses the health of her husband, former president Bill Clinton, at New York-Presbyterian Hospital.